For some time I have been plagued with a mysterious miss haunting my TBird.  All is good for a month or two, then out of the blue the engine develops a miss.  I clean the distributor cap, check the plugs, timing and wires and it goes away.  Last week it returned with a vengeance.  It was popping out the exhaust and running rough.  This time I believe I have found the culprit.

My car has it's original three speed manual transmission with overdrive and a 4.11 gear.  I have a 12 volt Pertronics unit in a 1957 distributor.  Overdrive transmissions use a kick down switch under the accelerator pedal.  This switch has a wire running to the coil that sends a momentary ground signal to the ignition to aid in dropping the transmission out of overdrive.   I believe the old kick down switch in my car was sending false signals to my ignition system causing the miss.

I never use the kick down switch.  I downshift manually if I need to pass. I disconnected the wire from the kick down switch to the distributor and went though the engine again.   I checked the valve lash and it was perfect.  I installed new plugs, distributor cap and rotor and retimed the engine. There was an immediate difference in the way my engine sounds and feels.  I believe the bad kickdown switch was causing a lot of other problems which may have become worse with the Pertronix unit.